i was thinking 5's, but possibly to a top (submax) weight for 2-3 sets

Good idea! When I started to do them, they made my lats crazy sore the days after from squeesing the bar towards the chins. It turned out to be one of my favorite assistance lifts for the deadlift since it really gets pull from the floor nailed down. When a deadlift fails, formwise, it all starts with a bad pull from the floor (bar to far from chins, hips moving up before bar etc)